Dual closed-loop chemical recycling support sustainable mitigation of plastic pollution

Abstract

Recently, the Feringa Nobel Prize Scientist Joint Research Center demonstrated a green method to synthesize plastics from natural small thioctic acid (TA) monomers. This novel recycling system provides successful chemical recycling using a dual closed-loop process under mild operating conditions. Here, we discuss the critical environmental sustainability dynamics of these recycling systems and their potential to support a plastic circular economy. Recently, the Feringa Nobel Prize Scientist Joint Research Center demonstrated a green method to synthesize plastics from natural small thioctic acid (TA) monomers. This novel recycling system provides successful chemical recycling using a dual closed-loop process under mild operating conditions. Here, we discuss the critical environmental sustainability dynamics of these recycling systems and their potential to support a plastic circular economy. Plastic pollution is widespread and affects a wide range of ecosystem types including atmospheric, aquatic, and terrestrial environments. Plastic pollution is an important driver of global environmental change due to their cascading effects on ecosystems, including impacts on safe drinking water and crop productivity.1Jia L. Evans S. Linden S.V. Motivating actions to mitigate plastic pollution.Nat. Commun. 2019; 10: 4582Crossref PubMed Scopus (39) Google Scholar, 2Bank M.S. Ok Y.S. Swarzenski P.W. Microplastic’s role in antibiotic resistance.Science. 2020; 369: 1315Crossref PubMed Google Scholar, 3Rillig M.C. Ryo M. Lehmann A. Aguilar-Trigueros C.A. Buchert S. Wulf A. Iwasaki A. Roy J. Yang G. The role of multiple global change factors in driving soil functions and microbial biodiversity.Science. 2019; 366: 886-890Crossref PubMed Scopus (186) Google Scholar By 2015, total global plastic waste was estimated to be4Geyer R. Jambeck J.R. Law K.L. Production, use, and fate of all plastics ever made.Sci. Adv. 2017; 3: e1700782Crossref PubMed Scopus (4364) Google Scholar 6,300 million metric tons (Mt) of which only 21% was incinerated or properly recycled while the remaining was either accumulated in landfills or released into the environment.4Geyer R. Jambeck J.R. Law K.L. Production, use, and fate of all plastics ever made.Sci. Adv. 2017; 3: e1700782Crossref PubMed Scopus (4364) Google Scholar Accordingly, at the current rate of production and management, approximately 12,000 Mt of plastic waste is destined for landfills or will be mismanaged by 2050.4Geyer R. Jambeck J.R. Law K.L. Production, use, and fate of all plastics ever made.Sci. Adv. 2017; 3: e1700782Crossref PubMed Scopus (4364) Google Scholar Primary macroplastic particles (>5 mm) often degrade into secondary microplastic (<5 mm and >100 nm) or nanoplastics (<100 nm) causing negative impacts on a wide array of ecosystem services.2Bank M.S. Ok Y.S. Swarzenski P.W. Microplastic’s role in antibiotic resistance.Science. 2020; 369: 1315Crossref PubMed Google Scholar,3Rillig M.C. Ryo M. Lehmann A. Aguilar-Trigueros C.A. Buchert S. Wulf A. Iwasaki A. Roy J. Yang G. The role of multiple global change factors in driving soil functions and microbial biodiversity.Science. 2019; 366: 886-890Crossref PubMed Scopus (186) Google Scholar Microplastics are widely distributed throughout the world’s ecosystems including remote, high-elevated sites such as Mount Everest.5Napper I.E. Davies B.F.R. Clifford H. Elvin S. Koldewey H.J. Mayewski P.A. Miner K.R. Potocki M. Elmore A.C. Gajurel A.P. et al.Reaching New Heights in Plastic Pollution—Preliminary Findings of Microplastics on Mount Everest.One Earth. 2020; 3: 621-631Abstract Full Text Full Text PDF Scopus (109) Google Scholar Americans unknowingly consume >50,000 microplastic particles per year,6Cox K.D. Covernton G.A. Davies H.L. Dower J.F. Juanes F. Dudas S.E. Human Consumption of Microplastics.Environ. Sci. Technol. 2019; 53: 7068-7074Crossref PubMed Scopus (535) Google Scholar and nanoplastic accumulation is reported in plants (i.e., Arabidopsis thaliana).7Sun X.D. Yuan X.Z. Jia Y. Feng L.J. Zhu F.P. Dong S.S. Liu J. Kong X. Tian H. Duan J.L. et al.Differentially charged nanoplastics demonstrate distinct accumulation in Arabidopsis thaliana.Nat. Nanotechnol. 2020; 15: 755-760Crossref PubMed Scopus (241) Google Scholar This global and ubiquitous distribution of micro and nanoplastics in the environment may accumulate in terrestrial and aquatic food webs, threatening ecosystems and potentially human health.6Cox K.D. Covernton G.A. Davies H.L. Dower J.F. Juanes F. Dudas S.E. Human Consumption of Microplastics.Environ. Sci. Technol. 2019; 53: 7068-7074Crossref PubMed Scopus (535) Google Scholar This biogeochemical cycle of micro and nanoplastics8Bank M.S. Hansson S.V. The Plastic Cycle: A Novel and Holistic Paradigm for the Anthropocene.Environ. Sci. Technol. 2019; 53: 7177-7179Crossref PubMed Scopus (74) Google Scholar implicates plastic pollution as a critical environmental challenge. These findings demonstrate not only the global and ubiquitous nature of plastic pollution but also the declaration of a “Plastic Wars” to mitigate effects on human and ecosystem health. These threats, including access to clean drinking water and food security, call for coordinated global monitoring, recovery, and management programs supported by sustainable investments, international cooperation, and innovation. Plastic pollution is amplified by its long environmental residence time and non-degradable persistence derived from petrochemicals. From a life cycle perspective, biodegradable plastics is a promising candidate for a plastic circular economy that reduces the environmental burdens at the end of the product’s lifetime. Bio-based plastics have recently gained support as a viable alternative to petroleum-based plastics due to their biodegradability and carbon neutral characteristics. However, the effects of depolymerization may negatively affect monomer quality during the recycling process when degradation occurs. Recently, Prof. Ben L. Feringa (awarded the 2016 Nobel Prize in Chemistry) from the East China University of Science and Technology and the University of Groningen in the Netherlands, invented a green method to synthesize two types of easily recyclable plastics using natural small thioctic acid (TA) monomers as precursors (Figure 1).9Zhang Q. Deng Y. Shi C.-Y. Feringa B.L. Tian H. Qu D.-H. Dual closed-loop chemical recycling of synthetic polymers by intrinsically reconfigurable poly(disulfides).Matter. 2021; 4 (this issue): 1352-1364https://doi.org/10.1016/j.matt.2021.01.014Abstract Full Text Full Text PDF Scopus (29) Google Scholar Interestingly, this novel method includes thermoplastic elastomers Poly(TA-M) and mechanically robust ionic films Poly(TA-Na)—both which were successful using a dual closed-loop chemical recycling system under mild operating conditions.9Zhang Q. Deng Y. Shi C.-Y. Feringa B.L. Tian H. Qu D.-H. Dual closed-loop chemical recycling of synthetic polymers by intrinsically reconfigurable poly(disulfides).Matter. 2021; 4 (this issue): 1352-1364https://doi.org/10.1016/j.matt.2021.01.014Abstract Full Text Full Text PDF Scopus (29) Google Scholar This work could ostensibly pave the way for efficient synthesizing of recyclable polymers in a simple, mild, organic solvent-free, and low-cost way that supports environmental sustainability and a plastic circular economy. These efforts have the potential to mitigate plastic pollution and support several of the relevant UN sustainable development goals (SDGs). Since the production and utilization of TA-based polymers has largely occurred in cities and urban areas, this proposed system will significantly accelerate the mitigation of plastic pollution to achieve the relevant SDGs, namely SDG 11 - Sustainable Cities and Communities and SDG 12 - Responsible Consumption and Production. Furthermore, plastic pollution is an environmental and societal problem that could be effectively mitigated through the application of this dual closed-loop chemical recycling system, which will also aid in achieving SDG 14 - Life below Water and SDG 15 - Life on Land. The TA polymer precursors are natural small-molecule monomers synthesized by plants, animals, and humans. The Poly(TA-M) and Poly(TA-Na) are synthesized using a solvent-free heat-induced ring-opening polymerization (ROP) in the presence of metal salts at 120°C and an evaporation-induced ROP in the presence of NaOH at 80°C, respectively.9Zhang Q. Deng Y. Shi C.-Y. Feringa B.L. Tian H. Qu D.-H. Dual closed-loop chemical recycling of synthetic polymers by intrinsically reconfigurable poly(disulfides).Matter. 2021; 4 (this issue): 1352-1364https://doi.org/10.1016/j.matt.2021.01.014Abstract Full Text Full Text PDF Scopus (29) Google Scholar The two-step treatment for chemical recycling of two types of TA-based polymers includes: (1) a ring-closing depolymerization using simple inorganic base as a catalyst and distilled water as a preferred solvent, and (2) a direct acidification separation with slow addition of acid.9Zhang Q. Deng Y. Shi C.-Y. Feringa B.L. Tian H. Qu D.-H. Dual closed-loop chemical recycling of synthetic polymers by intrinsically reconfigurable poly(disulfides).Matter. 2021; 4 (this issue): 1352-1364https://doi.org/10.1016/j.matt.2021.01.014Abstract Full Text Full Text PDF Scopus (29) Google Scholar The polymerization and chemical recycling operated at low temperatures, making clean renewable energy such as low-grade solar thermal energy or wind-power as applicable and clean heat sources. In addition, the additives (i.e., metal ions, etc.) could easily be separated in the acidification treatment, which is beneficial for practical applications of the plastic recycling process. Around 87% of the TA monomers are recovered in a pure form for efficient re-polymerization thereby creating fully recyclable plastics. The large-scale 100 g experiment for both polymerization and chemical recycling verify the practical industrial applications and support for a sustainable plastic circular economy. Considering the practical applications of these polymers synthesized in this effort, the performance of both origin and re-polymerized polymers exhibited excellent and consistent recoveries and mechanical function even after completing three cycles of chemical recycling.9Zhang Q. Deng Y. Shi C.-Y. Feringa B.L. Tian H. Qu D.-H. Dual closed-loop chemical recycling of synthetic polymers by intrinsically reconfigurable poly(disulfides).Matter. 2021; 4 (this issue): 1352-1364https://doi.org/10.1016/j.matt.2021.01.014Abstract Full Text Full Text PDF Scopus (29) Google Scholar Compared with the established concept of depolymerization and reprocessing, dual closed-loop chemical recycling is robust and environmentally friendly making the polymers more sustainable based on the simple, natural, and small TA molecule. This innovation is critically important to polymer science and society as it is a cost-effective mitigation strategy to address plastic pollution in a holistic manner. Most importantly, an evaluation of the overall recycling potential of TA-based polymers requires a comprehensive life cycle assessment (LCA) including detailed life cycle inventory (LCI) data. Approximately, 44 relevant LCA investigations, including environmental impacts for both bio-based and petroleum-based plastics published during 2011–2020,10Bishop G. Styles D. Lens P.N.L. Environmental performance comparison of bioplastics and petrochemical plastics: A review of life cycle assessment (LCA) methodological decisions.Resour. Conserv. Recycling. 2021; 168: 105451Crossref Scopus (48) Google Scholar question whether biodegradable plastics can support both sustainable ecosystems and a circular economy. The evaluation of environmental impacts from bio-based polymers requires comprehensive reporting of LCI data including all plastic additives in the LCI. In addition, plastic utilization cycles need to be incorporated using standardized functional unit definitions and system boundaries. Collectively, strategic support for environmental, social, and corporate governance (ESG) in the evaluation of TA-based polymers may encourage industrial mitigation of the unsustainable use of plastics. Dual closed-loop chemical recycling of synthetic polymers by intrinsically reconfigurable poly(disulfides)Zhang et al.MatterFebruary 4, 2021In BriefDeveloping repeatedly recyclable polymers is a timely and urgent task for chemists. An intrinsically reconfigurable polymer made from thioctic acid, a natural small molecule, is found to be a promising candidate for chemically recyclable polymers. Owing to the reversible nature of disulfide bond, the resulting poly(disulfides) can be easily and efficiently recycled by using basic aqueous solution. The reproduced materials exhibit fully recovered properties due to the virgin quality of the recycled monomers, showing the excellent recyclability and great prospects toward future green plastics. Full-Text PDF Open Archive